The present invention relates to a face panel of a color cathode ray tube.
FIG. 8 shows cross sections of a conventional color cathode ray tube (CRT). An upper half of the figure Is the cross section in a direction of a vertical axis V (referred to as a vertical cross section), and a lower half of the figure is the cross section in a direction of a horizontal axis H (referred to as a horizontal cross section). As shown in FIG. 8, the conventional color CRT has a face panel 1 (referred to as a panel 1), and a funnel 2 which constitutes an envelope of the CRT together with the panel 1. The color CRT also has a phosphor screen 3 comprising red, green, and blue phosphor dots orderly arranged and formed on an inner surface 10a of a face portion 10 of the panel 1, an electron gun 4 for emitting an electron beam 5, a deflection yoke 6 for electromagnetically deflecting the electron beam 5, and a tensioned shadow-mask 7 that functions as a color selection electrode. A perspective view of the tensioned shadow-mask 7 is schematically shown in FIG. 9.
Further, FIG. 10A shows cross sections of another conventional color CRT. An upper half of the figure is the vertical cross section, and a lower half of the figure is the horizontal cross section. FIG. 10B shows a perspective view of the color CRT of FIG. 10A. The color CRT shown in FIGS. 10A and 10B uses a pressed shadow-mask 77 having a surface curved in directions of vertical, horizontal and diagonal axes V, H and D. A perspective view of pressed the shadow-mask 77 is schematically shown in FIG. 11.
A high vacuum is maintained within the color CRTs of FIG. 8 and FIG. 10A by the envelope comprising the panel 1 and the funnel 2. When the electron beam 5 emitted from the electron gun 4 strikes on the phosphor screen 3 formed on the inner surface 10a of the face portion 10 of the panel 1, to which a high voltage is applied, the phosphor screen 3 emits light. At the same time, the electron beam 5 is deflected vertically and horizontally by a deflecting magnetic field generated by the deflection yoke 6, and forms on the phosphor screen 3 an image display area referred to as a raster. When red, green, and blue light from the image display area of the phosphor screen 3, intensity of which depends on intensity of the electron beam 5 impinging on the phosphor screen 3, is observed from an outside of the panel 1, an image is recognized.
The shadow-mask 7 (77) has a very large number of orderly arranged holes. The electron beam 5 passes through the hole so that it geometrically impinges on the red, green, or blue phosphor dot on the phosphor screen 3 at a predetermined location to perform accurate color selection. Since the color selection in the shadow-mask-type color CRT is geometrically performed, as has been described above, a predetermined positional relationship among the panel 1, the electron gun 4, and the shadow-mask 7 (77) must be accurately maintained.
In the conventional color CRTs of FIG. 8 and FIG. 10A formed as described above, the outer and inner surfaces 10b and 10a of the face portion 10 of the panel 1 on which the image display area is formed are curved so as to be convex toward the outside (that is, the outer surface 10b is convex and the inner surface 10a is concave) in order to resist the atmospheric pressure from the outside and maintain a high vacuum inside the color CRT. This, however, has caused several problems including the following: The displayed image is perceived convexly, the image is distorted when viewed obliquely, and portions of the image near the edges are hidden.
In order to solve these problems, a color CRT in which the image display area of the face portion of the panel is flat on its inner and outer surfaces was developed. This color CRT, however, requires a flat shadow-mask in order to keep accurately a predetermined positional relationship between the panel and the shadow-mask for the color selection, and such shadow-mask is very difficult to form. Due to the difference between the refractive index of the atmosphere and that of glass material of the panel, an image is perceived as being floated at the edges of the screen, that is, a displayed image is perceived concavely.